1. Field of the Invention
The present invention is directed to systems, processes and apparatus for selecting from between multiple power supplies for use with audio amplifiers. More particularly, the invention relates to the field of electronic musical instrument amplifiers that enable selection from between multiple power supplies to achieve differing sonic effects. Accordingly, the general objects of the invention are to provide novel systems, methods and apparatus of such character.
2. Description of the Related Art
The development of audio amplifiers from the early days of electronics has tracked the development in electronics components in many ways. For example, audio amplifiers, which originally used vacuum tubes as amplifying and rectifying elements, widely migrated to semiconductor elements soon after such elements became available. Nonetheless, the use of vacuum tubes persists in several niche applications such as hi-fi stereos, instrument amplification, recording pre-amplifiers, etc. due to a continuing and widespread belief that vacuum tubes produce superior results in such applications.
In the field of musical instrument amplifiers, certain “vintage” instrument amplifiers are much sought after for their ability to provide the sonic qualities of various well known and appreciated musical styles. Unfortunately, such vintage amplifiers typically have deteriorated with age and have become unreliable to the extent that use of such vintage devices is unacceptable. Even in those instances where the performance is satisfactory when measured against the original specifications for the equipment, musicians frequently find that such equipment is extremely limited by today's standards of versatility. There has, therefore, been a need for equipment capable of producing a range of tones of quality vintage equipment while at the same time providing the versatility and reliability more commonly associated with modern equipment. In order to meet this long standing and accelerating demand, vacuum tube amplification continues to progress around the periphery of a handful of basic designs in an effort to provide more economical, reliable, versatile and user-friendly amplifiers that offer musicians a choice of familiar sonic qualities.
Among the areas that have been the subject of such development has been preamp switching design, amplifier switching design, digital amplifier modeling technology, and power tube substitution schemes for vacuum tube guitar amplifiers. However, the sonic contribution of power supply design has only recently come under scrutiny among musicians and amplifier designers. In particular, the sonic contributions of such factors as, preamp bias voltage, power amp bias voltage, type of power amp biasing, the effects of various component types and sizes are being explored more closely.
This renewed interest in power supply design has yielded some efforts to provide more versatile power supplies to achieve varying musical effects. One such effort is described in U.S. Pat. No. 5,168,438, entitled Selectable Dual Rectifier Power Supply For Musical Amplifier, which describes a simple switching method for selecting from between either a solid-state rectifier or a vacuum thermionic rectifier within a single power supply. This approach offers a reasonably economical way of approximating the desirable characteristics of tube-based rectifiers with the desirable characteristics of solid-state rectifiers in a single amplifier. Unfortunately, this design trades certain subtle sonic qualities in favor of economy and simplicity in its approximation of both styles of power supplies. For example, since this design uses the same secondary power transformer coil and the same ripple-voltage filter regardless of the type of rectification selected only a limited range of changes are possible.
Another effort of this general type is disclosed in U.S. Pat. No. 5,091,700 and entitled Amplifier With Mains Voltage Reduction. This patent describes the use of a switch to adjust the mains voltage such that it is possible to reduce the voltages in an amplifier for a different musical effect. This switch adjusts the mains input voltage by selecting a primary winding tap on the primary side of a power transformer to thereby change all the voltages in the amplifier. While this design does appreciate that some transformer characteristics are important in creating the overall amplifier characteristics, its simplistic approach is incapable of changing a limited set of voltages while leaving others unaffected (or changed in the opposite direction). Thus, once again, this design offers economy and simplicity at the expense of some of the finer elements of the several vintage amplifiers it tries to approximate. For example, this design also uses the same secondary power transformer coil and the same ripple-voltage filter regardless of the type of rectification selected.
Yet another effort to offer a more versatile amplifier power supply for a vacuum tube amplifier is embodied in an amplifier known as the FENDER® PROSONIC®. This amplifier uses a switching system slightly more complicated than those noted above to offer a number a rectification options. Once again, however, this design also uses the same power transformer and the same ripple-voltage filter regardless of the rectification circuit selected. It, thus, also fails to appreciate the important role of transformer design in the overall amplifier characteristics.
All of the designs noted above suffer from the deficiency that they all sacrifice some degree of sound quality in an effort to provide approximations of the sonic qualities of multiple amplifiers. Thus, after many years, no amplifier design has been able to faithfully emulate the essential characteristics of several different vintage amplifiers in one simple, economical, reliable and user-friendly amplifier.
There is, accordingly, a need in the art for novel methods, systems and apparatus that faithfully emulate the desired characteristics of several vintage amplifiers in one simple, economical, reliable and user-friendly package. Such methods and apparatus should go further than prior efforts in capturing various subtle qualities of various amplifier designs without presenting users with undue additional complexity, weight size and/or expense.